In a recent series of papers, we introduced a new model of nucleosynthesis in which the matter content of the universe came into existence at a time of about 4 × 10-5 s. At that time, a small percentage of the vacuum energy was converted into neutron/antineutron pairs with a very small excess of neutrons. This process was regulated by an imprint that was established in the vacuum during an initial Plank-era inflation. Immediately after their inception, annihilation and charge exchange reactions proceeded at a very high rate and ran to completion after an interval of about 10-11 s. By then, all the antibaryons had disappeared thereby establishing the matter/antimatter asymmetry of the universe. What remained were very high densities of mesons and leptons, somewhat lower densities of protons and neutrons, and finally, the very high density of photons that eventually became the CMB. The density of matter so created varied from one location to another in such a manner as to account for all cosmic structures and because the energy density of the photons varied in proportion to that of the matter, the CMB-to-be came into existence with an anisotropic spectrum already in place. For structures, the size of galaxy clusters, the initial anisotropy magnitudes were on the order of 25%. In this paper, we will follow the subsequent evolution of the photons and show that this model predicts with accuracy the temperature of the warmest anisotropies in the observed CMB spectrum. .
Background: When applied to trabecular bone X-ray images, the anisotropic properties of trabeculae located at ultra-distal radius were investigated by using the trabecular bone scores (TBS) calculated along directions parallel and perpendicular to the forearm. Methodology: Data from more than two hundred subjects were studied retrospectively. A DXA (GE Lunar Prodigy) scan of the forearm was performed on each subject to measure the bone mineral density (BMD) value at the location of ultra-distal radius, and an X-ray digital image of the same forearm was taken on the same day. The values of trabecular bone score along the direction perpendicular to the forearm, TBSx, and along the direction parallel to the forearm, TBSy, were calculated respectively. The statistics of TBSx and TBSy were calculated, and the anisotropy of the trabecular bone, which was defined as the ratio of TBSy to TBSx and changed with subjects’ BMD and age, was reported and analyzed. Results: The results show that the correlation coefficient between TBSx and TBSy was 0.72 (p BMD and age was reported. The results showed that decreased trabecular bone anisotropy was associated with deceased BMD and increased age in the subject group. Conclusions: This study shows that decreased trabecular bone anisotropy was associated with decreased BMD and increased age.
Optical reflection anisotropy microscopy mappings of micropipe defects on the surface of a 4H-SiC single crystal are studied by the scanning anisotropy microscopy(SAM)system.The reflection anisotropy(RA)image with a'butterfly pattern'is obtained around the micropipes by SAM.The RA image of the edge dislocations is theoretically simulated based on dislocation theory and the photoelastic principle.By comparing with the Raman spectrum,it is verified that the micropipes consist of edge dislocations.The different patterns of the RA images are due to the different orientations of the Burgers vectors.Besides,the strain distribution of the micropipes is also deduced.One can identify the dislocation type,the direction of the Burgers vector and the optical anisotropy from the RA image by using SAM.Therefore,SAM is an ideal tool to measure the optical anisotropy induced by the strain field around a defect.
Qingshankou shale(Gulong area,China)exhibits strong acoustic anisotropy characteristics,posing significant challenges to its exploration and development.In this study,the five full elastic constants and multipole response law of the Qingshankou shale were studied using experimental measurements.Analyses show that the anisotropy parametersϵandγin the study region are greater than 0.4,whereas the anisotropy parameterδis smaller,generally 0.1.Numerical simulations show that the longitudinal and transverse wave velocities of these strong anisotropic rocks vary significantly with inclination angle,and significant differences in group velocity and phase velocity are also present.Acoustic logging measures the group velocity in dipped boreholes;this differs from the phase velocity to some extent.As the dip angle increases,the longitudinal and SH wave velocities increase accordingly,while the qSV-wave velocity initially increases and then decreases,reaching its maximum value at a dip of approximately 40°.These results provide an effective guide for the correction and modeling of acoustic logging time differences in the region.
Li Qing-fengYan Xue-hongYan Wei-linRen LiWang PengHan Jian-qiangXia XueChen Hao
Rheology of rocks controls the deformation of the Earth at various space-time scales,which is crucial to understand the tectonic evolution of continental lithosphere.Researches of rock rheology are mainly conducted via high-pressure and hightemperature rheological experiments and multi-scale observations and measurements of naturally deformed rocks.At present,a large amount of data from such kinds of studies have been accumulated.This paper first provides an up-to-date comprehensive review of the rheological mechanisms,fabric types and seismic properties of the main rock-forming minerals at different depths of continental lithosphere,including olivine,orthopyroxene,clinopyroxene,amphibole,plagioclase,quartz and mica.Then,progress in high-pressure and high-temperature experiments and natural deformation observations is introduced,mainly regarding the rheological strength and behavior,seismic velocity and anisotropy of lithospheric mantle peridotite,eclogite,mafic granulite,amphibolite and felsic rocks.Finally,by taking the Tibetan Plateau as an example,the application of rock rheology for quantitative interpretation of seismic anisotropy data is discussed.The combination of mineral deformation fabrics and seismic anisotropy is expected to make an important breakthrough in understanding the rheological properties and structure of continental lithosphere.
The presentation and modeling of turbulence anisotropy are crucial for studying large-scale turbulence structures and constructing turbulence models.However,accurately capturing anisotropic Reynolds stresses often relies on expensive direct numerical simulations(DNS).Recently,a hot topic in data-driven turbulence modeling is how to acquire accurate Reynolds stresses by the Reynolds-averaged Navier-Stokes(RANS)simulation and a limited amount of data from DNS.Many existing studies use mean flow characteristics as the input features of machine learning models to predict high-fidelity Reynolds stresses,but these approaches still lack robust generalization capabilities.In this paper,a deep neural network(DNN)is employed to build a model,mapping from tensor invariants of RANS mean flow features to the anisotropy invariants of high-fidelity Reynolds stresses.From the aspects of tensor analysis and input-output feature design,we try to enhance the generalization of the model while preserving invariance.A functional framework of Reynolds stress anisotropy invariants is derived theoretically.Complete irreducible invariants are then constructed from a tensor group,serving as alternative input features for DNN.Additionally,we propose a feature selection method based on the Fourier transform of periodic flows.The results demonstrate that the data-driven model achieves a high level of accuracy in predicting turbulence anisotropy of flows over periodic hills and converging-diverging channels.Moreover,the well-trained model exhibits strong generalization capabilities concerning various shapes and higher Reynolds numbers.This approach can also provide valuable insights for feature selection and data generation for data-driven turbulence models.
Two-dimensional(2D)anisotropic materials have garnered significant attention in the realm of anisotropic optoelectronic devices due to their remarkable electrical,optical,thermal,and mechanical properties.While extensive research has delved into the optical and electrical characteristics of these materials,there remains a need for further exploration to identify novel materials and structures capable of fulfilling device requirements under various conditions.Here,we employ heterojunction interface engineering with black phosphorus(BP)to disrupt the C_(3) rotational symmetry of monolayer WS_(2).The resulting WS_(2)/BP heterostructure exhibits pronounced anisotropy in exciton emissions,with a measured anisotropic ratio of 1.84 for neutral excitons.Through a comprehensive analysis of magnetic-field-dependent and temperature-evolution photoluminescence spectra,we discern varying trends in the polarization ratio,notably observing a substantial anisotropy ratio of 1.94 at a temperature of 1.6 K and a magnetic field of 9 T.This dynamic behavior is attributed to the susceptibility of the WS_(2)/BP heterostructure interface strain to fluctuations in magnetic fields and temperatures.These findings provide valuable insights into the design of anisotropic optoelectronic devices capable of adaptation to a range of magnetic fields and temperatures,thereby advancing the frontier of material-driven device engineering.
Xinran LiXing XieBiao WuJunying ChenShaofei LiJun HeZongwen LiuJian-Tao WangYanping Liu
In rehabilitation training,it is crucial to consider the compatibility between exoskeletons and human legs in motion.However,most exoskeletons today adopt an anthropomorphic serial structure,which results in rotational centers that are not precisely aligned with the center of the hip joint.To address this issue,we introduce a novel exoskeleton called the Parallel Hip Exoskeleton(PH-Exo)in this paper.PH-Exo is meticulously designed based on the anisotropic law of output torque.Considering the friction of the drive components,a dynamic model of the human-machine complex is established.Simulation analysis demonstrates that PH-Exo not only exhibits outstanding torque performance but also achieves high controllability in both flexion/extension and adduction/abduction directions.Additionally,a robust controller is designed to address model uncertainty,friction,and external interference.Wearing experiments indicate that under the control of the robust controller,each motor achieves excellent tracking performance.
Two-dimensional(2D)transition metal dichalcogenides(TMDs)have garnered considerable attention for their promising applications in sensors and optoelectronic devices,owing to their exceptional optical,electronic,and optoelectronic properties.However,the inherent high symmetry of TMD lattices imposes limitations on their functional versatility.Here,we present a strategy to disrupt the C_(3)rotational symmetry of monolayer WSe_(2)by fabricating a heterostructure incorporating WSe_(2)and SiP flakes.Through comprehensive experimental investigations and first-principle calculations,we elucidate that in the WSe_(2)/SiP heterostructure,excitons-both neutral and charged-emanating from WSe_(2)exhibit pronounced anisotropy,which remains robust against temperature variations.Notably,we observe an anisotropic ratio reaching up to 1.5,indicating a substantial degree of anisotropy.Furthermore,we demonstrate the tunability of exciton anisotropy through the application of a magnetic field,resulting in a significant reduction in the anisotropic ratio with increasing field strength,from 1.57 to 1.18.Remarkably,the change in heterojunction anisotropy ratio reaches 24.8%as the magnetic field increases.Our findings elucidate that the perturbation of the C_(3)rotational symmetry of the WSe_(2)monolayer arises from a non-uniform charge density distribution within the layer,exhibiting mirror symmetry.These results underscore the potential of heterostructure engineering in tailoring the properties of isotropic materials and provide a promising avenue for advancing the application of anisotropic devices across various fields.
Biqi HuXing XieXinyu OuyangJunying ChenShaofei LiJun HeZongwen LiuJian-Tao WangYanping Liu
